T84 Synchro?

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Frankie
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T84 Synchro?

Post by Frankie » Sat Feb 24, 2018 7:39 am

The Synchro that I took out of my H case T84 is very difficult to move the sleeve on the hub; it takes two hands and a lot of pressure to move the sleeve at all and the parts are well lubed. I had the transmission completely assembled and could not move the 2-3 shift fork at all. I'm thinking the synchro is defective? In my stash of old parts I found a compete synchro and the hub and sleeve move easily. I see no signs of wear on the old used synchro; would this be a good candidate to install in the T84? Not really wanting to buy a new one. Thanks, Frank


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Re: T84 Synchro?

Post by Frankie » Sat Feb 24, 2018 8:52 am

Sorry, I meant only the hub and sleeve. No springs or shifter plates installed

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Chuck Lutz
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Re: T84 Synchro?

Post by Chuck Lutz » Sat Feb 24, 2018 9:10 am

1) you stated the synchro assembly you removed from the H case is difficult to slide the sleeve on when held in your hands, right?
2) did this transmission have shifting difficulties before the rebuild?
3) you stated you found no signs of wear/damage to the hub or the sleeve, right?
4) you stated that it was difficult without the two springs and three shift plates, right?

You might consider using the "old" synchro assembly you found in your parts stash.....but wear on the sleeve or the hub splines should be checked out. Likewise, compare the three shift plates in the one you have problems with to those in the parts stash assembly.

5) where did these two synchro assemblies come from...if you happen to know?
6) was that "H" T-84 rebuilt at any time in the past to your knowledge and...did it perform as it should when installed in the jeep?
7) did you attempt to try swap the sleeves from one assembly to the other to identify if the problem is the sleeve or the hub?
8) when assembled with either synchro, did you find it impossible to move the 2-3 shift fork or just with one of them?
9) If you align the teeth on the sleeve with those on the blocking ring when installed in the case, is it still impossible to engage either gear?
10) how much "slop" is there on both the 2nd and 3rd gear blocking rings once assembled?
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947

Frankie
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Re: T84 Synchro?

Post by Frankie » Sat Feb 24, 2018 10:14 am

1 right, very difficult to move
2 unknown. It had maybe a tablespoon of water when draining the oil, so I decided to disassemble to check for damage, I have owned the jeep about 20 years, have never driven it.
3 right
4 right
5 the synchro that I took out was in in when I bought it. The used one I don't recall where it came from, but is complete with springs and shift plates
6 unknown, but I suspect possible rebuild before 1998 as the synchro and blocking rings appear to be exc/very good condition while the 1st/reverse gear had wear and was replaced by me
7 I have not swapped parts from one synchro to another
8 with the tight synchro, assembled transmission, it was nearly impossible to move the 2/3 shift fork, even with leverage. Have not tried the used looser one
9 same as 8
10 less than .010 (guess)

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Re: T84 Synchro?

Post by artificer » Sat Feb 24, 2018 10:59 am

Like all problems we diagnose the issue & eliminate what is not the causing the same.

Before being pulled apart was this similar tight/locking condition evident? Always check these type things before getting into things. One example most would understand is before pulling a differential apart, check the contact pattern.

Why are the synchro sleeve & hub assy in the transmission without the springs or shifter plates installed?

When splined parts are taken apart then put back together, they should be assembled in exactly the same way/position.
Not doing so can exhibit this current issue.

With the shifter plates out the sleeve & hub should slide freely on one another.
If they don't, first I would be checking for burrs on the spline/s.
If none, I would be reindexing the the splines until the 2 components do slide easily then installing the shifter plates & springs.

Once this optimal mating is achieved one knows the syncho hub & sleeve assy is not the problem.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: T84 Synchro?

Post by Frankie » Sat Feb 24, 2018 11:36 am

Thanks for your response. I did not check the synchro function before removing, so have no idea if there was a prior problem. At the time I removed the synchro, the springs and shift plates were installed. I also did not mark the original alignment, alas. I looked for burrs but found none, also tried indexing the hub and sleeve but did not find an alignment that allowed the parts to move easily. At this point, I plan to reinspect the hub and sleeve for burrs, then try again to find a fit that allows easier sliding. If I can not find a fit, then I plan to try the older used synchro. Meanwhile, I'll also try to get quality pics of both synchros so they can be analyzed.

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Re: T84 Synchro?

Post by artificer » Sat Feb 24, 2018 12:20 pm

See PM
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

Frankie
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Re: T84 Synchro?

Post by Frankie » Sat Feb 24, 2018 1:18 pm

Hello! Thanks to your postings, I went down, tried indexing the hub and sleeve and found a sweet spot where they slide easily. I marked it so I can reassemble in the same spot. It is truly amazing how easily it slides in one place but one spline off in either direction it becomes difficult. Thanks for all your responses! :D

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Re: T84 Synchro?

Post by artificer » Sat Feb 24, 2018 11:50 pm

Frankie wrote:
Sat Feb 24, 2018 1:18 pm
Hello! Thanks to your postings, I went down, tried indexing the hub and sleeve and found a sweet spot where they slide easily. I marked it so I can reassemble in the same spot. It is truly amazing how easily it slides in one place but one spline off in either direction it becomes difficult. Thanks for all your responses! :D
Obviously learned practice over a long period shows self taught/made/proclaimed experts, who don't believe parts that have worn together need replacing the same way, don't have all the answers
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: T84 Synchro?

Post by old arkie » Tue Oct 09, 2018 1:04 pm

JUST tried using the black repo spring plates. in the sycro hub and found they will not fit in as to wide. not sure when or where I got them but sure they were in one of the small parts kit. I am trying to find a set of the original ones will buy 1 or more if available, desperate thanks

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Re: T84 Synchro?

Post by Chuck Lutz » Wed Oct 10, 2018 9:30 am

You are not alone. Small parts kits for the T84 have been known to have the same problems as you have experienced.
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947

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Re: T84 Synchro?

Post by old arkie » Wed Oct 10, 2018 3:54 pm

not good news and the cost of a small parts kit jut to have one gets costly. So I took the broken one and entered tot he trash can. then filed down the edges of the best one until it slipped into place. bout filed off my fingernail holding it. put all back into the case and it seem to work okay but still hoping to find original ones any ideas for a search???


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